Among the vertebrates, a few species of frogs and reptiles have evolved the unique capacity to tolerate extensive ice formation within their bodies during hibernation. Wood frogs (Rana sylvatica) and box turtles (Terrapene carolina) routinely survive the freezing of up to 65% of their total body water. Freezing is accompanied by the accumulation of large amounts of ice within the abdominal cavity and beneath the skin. The water for this ice comes from the extensive dehydration of organs; some lose nearly 60% of their initial water. Within minutes after freezing begins, large amounts of glucose are produced by the liver, and blood and tissue glucose levels continue to rise for the next 5-10 hours. Freezing is accompanied by the release of the heat of crystallization which elevates body temperature and causes an increase in the heart rate for at least 10 hours. The proposed research will focus on two hypotheses. The first is that organ dehydration promotes survival. To test this proposition, experiments will attempt to determine: the limits and time-courses of dehydration during freezing and rehydration upon thawing in major organs during freezing; the extent to which dehydration reduces the amount of ice that forms within the body and organs; whether perfusion of organs is required for effective dehydration and subsequent rehydration during the freeze-thaw cycle, or, whether water flux can occur independently of the circulatory system; the consequence of freezing-induced organ dehydration on plasma and tissue osmotic concentrations, pH, levels of anaerobic metabolites, and electrolytes. The second hypothesis is that glucose functions as a cryoprotectant during freezing. Studies to be conducted in this regard relate to: how survival, at the cellular and organismal levels of organization, is related to the concentration of glucose in plasma and major organs; the extent to which glucose reduces the amount of ice that forms within the body and organs; whether the distribution of glucose from the liver to tissues and organs is dependent upon tissue perfusion; whether the cardioacceleratory response initiated by ice formation facilitates the distribution of glucose. Currently, it is not possible to cryopreserve human organs. Obviously, freeze-tolerant frogs and turtles have "solved" not only the problem of successfully freezing individual organs, but that of freezing multiple organs simultaneously. Studies of the mechanisms by which these animals survive extensive ice formation within their bodies may provide valuable cues for the development of successful methods for the cryopreservation and banking of human organs. Additionally, this research could conceivably provide important insight into significant biomedical problems related to water and electrolyte balance, cold exposure, glucose metabolism, and hypoxia.